Swede Momsen: Diving & Rescue - Rescue Chamber

Momsen, traumatized by the sinking of the S-51 and learning that the men had survived the wreck only to be trapped inside the submarine at the ocean's bottom, thought of a way to rescue trapped Submariners. He would build a large steel bell-shaped chamber, which could be lowered with cables down to the escape hatch on a sunken submarine. A watertight seal to the submarine could be achieved by placing a rubber gasket around the diving bell's bottom and reducing the air pressure once the bell was over the escape hatch. Then, the hatch could be opened, and the trapped Submariners could climb aboard. A hatch on the top of the bell would allow the rescued Submariners and diving bell operators an easy way out of the bell.

The diving bell went through a series of tests off the shores of Key West, Florida. Based on these tests, Momsen had several changes in mind for the bell, but was sent to the Bureau of Construction and Repair to teach Submariners how to use the Momsen Lung before he could make the changes. Lieutenant Commander Allan McCann was put in charge of the revisions on the diving bell. When the bell was completed in late 1930, it was introduced as the McCann Rescue Chamber.